CA R CR AZY
What’s so good about cars? Cars are chemistry labs on wheels. And though that might not sound so interesting, it accounts absolutely for their ubiquity. Take away the leather seats, the gleaming chrome, the go-faster stripes and all the rest, and you’re left with a handful of tin cans called cylinders, where petrol explodes into power. Cars are built around engines, and engines (or internal combustion engines, to give them their full name) burn petrol with oxygen in the air to release the energy locked inside it.We think of burning as a way of making fire, but it’s essentially a chemical reaction between oxygen and fuel that just happens to produce heat and fire as a by-product. The simple science of cars is so utterly mundane that we scarcely give it a thought: pump the petrol in your tank, turn the key and off you go.Think about it more closely, however, and you’ll see how astonishing it really is. Suppose a typical modern family car does about 40 miles to the gallon or, in metric terms, 100 km for every 7 litres of fuel.That means if you have a teaspoon of petrol (about 0.004 litres), it contains enough energy to roll your car about 60 m (200 ft), or roughly 15 times the car’s own length. Consider how hard it is to push a car, even once you’ve got it going from a standstill, and I’m sure you’ll agree that’s quite remarkable. The simple fact is that petrol is absolutely chock full of energy: short of uranium (nuclear fuel), it’s just about the most energy-rich material there is. That, more than any other reason – including the freedom, independence and social status that cars give us – accounts for their popularity. DEEP BREATHS Motorists learn never to go far without glancing at the fuel gauge: the Law of Conservation of Energy tells us cars go nowhere without the energy packed in petrol to power ▷
Atoms under the Floorboard.indb 75
1/27/2015 8:39:50 PM
Seriously surprising science from the sofa!